Light sources are used everywhere to produce light. Examples are indoor/outdoor lamps, TVs, traffic signs, commercial displays, car headlights/taillights, etc. a code, i.e. digital information, may be incorporated into the emitted light by modulating the light source, turning them on and off. This principle may be referred to as Visible Light Communication or VLC. When the modulation is fast enough, i.e. turning the light source on and off is done rapidly, the incorporation of digital information into the emitted light is unperceivable to the human eye.
Hence, VLC uses the phenomenon that if a frequency of an intermittent light stimulus is above a so-called flicker fusion threshold, the intermittent light stimulus appears to be completely steady to the average human observer. However, as the ability to detect flicker is dependent amongst other on physiological factors of the human observer such as age and fatigue, there is still a high risk of a human observer detecting flicker in current VLC systems. Further, even if no flicker is observed, the modulation of the light source might cause nausea.
Besides the negative effects on human observers, the modulation of the light source might interfere with optical read-out apparatus, e.g. bar-code readers, smartphone cameras, etc., which receive the light emitted by the light source while detecting other codes and information such as bar codes.